In an industrial plant, control devices are used for example for controlling transport systems, for controlling tools, such as welding tools, screwing and/or drilling tools, riveting tools, etc., for controlling sensors, controlling actuators, such as linear motors and rotary machines, etc. Normally, actions or tasks and thus the control of a component of the industrial plant to be controlled, such as a tool, are dependent on actions or results of another component of the industrial plant. Therefore, there is often a requirement that a data transmission takes place in real time between the control device and the components of the industrial plant to be controlled. In accordance with the DIN 44300 standard (Information Processing), part 9 (Processing sequences) now superseded by DIN ISO/IEC 2382, the real-time operation of a computing system is understood to mean one in which programs for processing incoming data are constantly operationally ready, such that the processing results are available within a specified time interval. Depending on the specific application case the data can accrue according to a temporally random distribution or at predetermined times.
In real-time capable networks, the transmission of time-critical data packets must be guaranteed within a specific time frame. In many real-time systems, this time window is defined by communication cycles, in which data are exchanged periodically or cyclically.
The reception of data packets must generally not be delayed beyond this time window. In the real-time capable networks it is therefore ensured that valid control data and status information are available at specific times and can be further processed.
In industrial automation as an example of real-time capable networks, control and status data are continuously exchanged between a central control device and a plurality of sensors or actuators. In this case the important criteria are real-time capability with guaranteed maximum transmission times and a high reliability of the data. As a result, the data transmission procedure must ensure that data are successfully delivered at a particular time.
A serious problem, however, is that in many real-time enabled networks the available transmission capacity is not fully exploited by only one single time-critical service. The rest of the transmission capacity can be used, among other things, for a transmission of additional, non-time-critical data to the same network node and/or a transmission of time-critical and non-time-critical data to other network nodes in the same transmission medium and/or transmission pauses to reduce the energy consumption. The time frame and the allocation of the transmission capacity are usually performed by a central controller.
In the current transmission methods, such as Sercos III, EtherCAT, Profinet, etc., data packet transmission errors cannot be completely eliminated. Depending on the transmission medium, such as unshielded cable or wireless transmission, and possibly shortened data transmission cycle times, one or more packet errors can occur in succession. This cannot be handled with the currently available error correction techniques, so that in the worst case the packet errors can lead to the failure of at least one component of the industrial plant or even the entire industrial plant. As a result, costly downtimes of the industrial plant are incurred.